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https://github.com/golang/go
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d8f7a64519
Use actual unmapped memory instead of small integers to make pointers that will fault when accessed. Fixes #49562 Change-Id: I2c60c97cf80494dd962a07d10cfeaff6a00f4f8e Reviewed-on: https://go-review.googlesource.com/c/go/+/364914 Trust: Keith Randall <khr@golang.org> Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
71 lines
1.9 KiB
Go
71 lines
1.9 KiB
Go
// run
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// +build linux darwin
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// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This is an optimization check. We want to make sure that we compare
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// string lengths, and other scalar fields, before checking string
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// contents. There's no way to verify this in the language, and
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// codegen tests in test/codegen can't really detect ordering
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// optimizations like this. Instead, we generate invalid strings with
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// bad backing store pointers but nonzero length, so we can check that
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// the backing store never gets compared.
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//
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// We use two different bad strings so that pointer comparisons of
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// backing store pointers fail.
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package main
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import (
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"fmt"
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"reflect"
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"syscall"
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"unsafe"
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)
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type SI struct {
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s string
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i int
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}
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type SS struct {
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s string
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t string
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}
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func main() {
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bad1 := "foo"
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bad2 := "foo"
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p := syscall.Getpagesize()
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b, err := syscall.Mmap(-1, 0, p, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANON|syscall.MAP_PRIVATE)
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if err != nil {
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panic(err)
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}
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err = syscall.Mprotect(b, syscall.PROT_NONE)
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if err != nil {
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panic(err)
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}
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// write inaccessible pointers as the data fields of bad1 and bad2.
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(*reflect.StringHeader)(unsafe.Pointer(&bad1)).Data = uintptr(unsafe.Pointer(&b[0]))
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(*reflect.StringHeader)(unsafe.Pointer(&bad2)).Data = uintptr(unsafe.Pointer(&b[1]))
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for _, test := range []struct {
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a, b interface{}
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}{
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{SI{s: bad1, i: 1}, SI{s: bad2, i: 2}},
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{SS{s: bad1, t: "a"}, SS{s: bad2, t: "aa"}},
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{SS{s: "a", t: bad1}, SS{s: "b", t: bad2}},
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// This one would panic because the length of both strings match, and we check
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// the body of the bad strings before the body of the good strings.
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//{SS{s: bad1, t: "a"}, SS{s: bad2, t: "b"}},
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} {
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if test.a == test.b {
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panic(fmt.Sprintf("values %#v and %#v should not be equal", test.a, test.b))
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}
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}
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}
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